1. Field of the Invention
The present invention relates to working fluid medium temperature control systems and methods.
2. Background Art
An electrohydraulic system, such as an electrohydraulic power-assist steering system, is known, which performs preheating of a working fluid medium.
In an example of such an electrohydraulic power-assist steering system for a vehicle, disclosed in JP 2008-273361, the main body of an electric motor is heated by turning on electricity even when rotation of the motor, which drives a hydraulic power steering pump, is stopped under static steering condition in the vicinity of neutral point while the vehicle is driving straight ahead. As a result, the heat generated by the electric motor is transferred to the working fluid medium passing through a fluid passage outside the motor, thereby to perform the preheating.
However, according to the technology disclosed in JP 2008-273361, the fluid passage is formed between the electric motor and a thin-walled sleeve surrounding the electric motor and meanders in such a way that the working fluid medium can stay in contact with the electric motor for a long time. With this passage structure, heat is quickly radiated from the working fluid medium because the heat is transmitted to the thin-walled sleeve exposed to the open air. As a result, the temperature of the working fluid medium changes greatly due to the repetition of heating and radiation cycle. Therefore, since the viscosity of the working fluid medium changes with the temperature change, it is possible that, with the same steering input, the power assist may differ substantially.
Therefore, there is a need for improving stability of operation of an actuator operable on a working fluid medium.
An object of the present invention is to provide a working fluid medium temperature control system, which can improve stability of operation of an actuator operable on the working fluid medium.